Field
The present disclosure generally relates to ground vibration testing of large flexible structures, such as aircraft. More specifically, the present disclosure generally relates to a system and method for the positioning and alignment of an adjustable electrodynamic shaker system with a test article or structure of an aircraft.
Description of the Related Art
Ground vibration testing of an aircraft is performed to determine the structural vibration properties (e.g., modal frequencies, vectors, damping) of the aircraft. These properties are then compared to values predicted by an analytical model, and the test results are used to refine the model to improve the model's fidelity. The model is subsequently used to assess the likelihood of flutter onset in response to applied aerodynamic forces. Once analysis is complete and the predictions show that flutter is unlikely, the aircraft is flown by pilots who attempt to induce a flutter response under a spectrum of load, airspeed, and altitude conditions. This spectrum encompasses the entire flight envelope as well as points outside of this envelope to demonstrate conclusively that the aircraft is free from flutter.
During ground vibration testing, electrodynamic shakers may be coupled to the aircraft to provide excitation input (e.g., vibration) to the aircraft. The dynamic response of the aircraft to the excitation input may be measured using sensors (e.g., accelerometers) mounted at various locations on the aircraft. The dynamic response may be analyzed and structural dynamic properties (e.g., frequencies, damping, and modal vectors) may be computed. These results are compared to values predicted by a structural dynamic analysis of the aircraft. The results of the comparison may be used to validate and/or refine the structural dynamic analysis model of a given aircraft.
Aircraft ground vibration tests utilize electrodynamic shakers positioned and aligned with respect to designated points on the aircraft surface. The electrodynamic shaker is positioned and aligned such that the central axis of the electrodynamic shaker is perpendicular to the test surface. Positioning and aligning electrodynamic shakers is difficult in that they oftentimes weigh over 400 pounds and may rest on elevated platforms exceeding 20 feet above the surface. Traditionally, a base of the electrodynamic shaker rests on the platform and is positioned in place via brute force before the position of the electrodynamic shaker is fine-tuned via a hammer. With such limitations, the positioning of the electrodynamic shaker is time consuming, ergonomically unfriendly, and risks damage to the aircraft and surroundings.
Therefore, what is needed in the art is a system and method for precisely positioning an electrodynamic shaker system in a reduced amount of time under a test article of an aircraft and which minimizes the level of risk of damage to the aircraft and staff.